1. Field of the Invention
The present invention relates to a data backup method for a storage system and, more specifically, to a data backup method with application of a so-called differential snapshot technology.
2. Description of the Related Art
For protection of data in a storage system, various types of technologies are known for continuously backing up the data.
As an example, Patent Document 1 (JP-A-2002-373093) describes the technology of copying a memory area (logical volume) in its entirety at the time of designation, and keeping the resulting copy as backup data. With such a technology, two logical volumes (logical disks in Patent Document 1) configure a mirror. Out of the two logical disks, when a positive logical volume (master logical disk in Patent Document 1) is written with data by a host computer, the data is also written into a sub logical volume (snapshot logical disk in Patent Document 1). When the mirror is disassembled, the snapshot logical disk carries therein the copy of the entire master logical disk at the time of disassembly of the mirror.
Patent Document 2 (JP-A-2003-280825) describes the technology of keeping differential data as backup data. Specifically, when any data stored in a positive logical volume (master storage in Patent Document 2) is updated, only the updated portion of the data, i.e., differential data, is copied into a sub logical volume (pile storage in Patent Document 2), and the resulting copy is kept therein. By combining the updated data in the master storage with the differential data in the pile storage, the data in the master storage before update can be restored.